This invention relates to the technical field of image display devices such as liquid-crystal displays and CRTs (cathode-ray tubes). More particularly, the invention relates to a method capable of displaying high-quality images without artifacts and flicker even if the image data has a higher gradation resolution than the display to be finally produced. The invention also relates to an apparatus for implementing the method.
The diagnostic images taken with medical diagnostic apparatus such as MRI diagnostic apparatus, X-ray diagnostic apparatus and CR (Computed Radiography) diagnostic apparatus such as FCR (Fuji Computed Radiography) are usually recorded on light-transmitting image recording films such as X-ray films and light-sensitive materials in film form and thereafter reproduced as light-transmissive images. The films showing the reproduced diagnostic images are set on a light source device called a light box (xe2x80x9cSchaukastenxe2x80x9d) and illuminated with a backlight so that the images are viewed for diagnostic purposes.
Medical diagnostic apparatus usually have a monitor (display) such as CRT or a liquid-crystal display (LCD), either built-in or connected, for viewing the diagnostic images taken with the apparatus. Diagnosis is performed on the basis of the image output to the monitor or the diagnostic images yet to be output on films are checked, adjusted or otherwise processed on the monitor.
Diagnostic images taken with medical diagnostic apparatus are usually reproduced on films at a gradation resolution of 10 bits. On the other hand, CRTs usually display images at a gradation resolution of 8 bits and LCDs usually display images at a gradation resolution of 6 bits, sometimes at 8 bits if they are of high performance. Driver ICs (integrated circuits) in excess of 8 bits are not currently available for LCDs. Thus, whichever of the monitors in current use display images with image data having a lower gradation resolution than the image data that has been output from medical diagnostic apparatus.
If images are to be displayed at the usual brightness in the range between about 100 cd/m2 and 200 cd/m2, the lower gradation resolution of 8 bits does not cause any serious problem. However, if the brightness of image display increases, the brightness resolution by human eyes (their ability to distinguish between dark and light areas) also increases and the forced reduction in gradation resolution often causes problematic artifacts in contour lines which are commonly called pseudo-contours.
The medical diagnostic images contemplated by the invention are monochromatic and depend on the difference in image density for diagnosis. To achieve correct diagnosis, it is required that subtle differences in density be identified even in high-density areas with densities in excess of 2. To meet this requirement, the light box emits very bright light, for example, at a brightness of 3,000 cd/m2 or more in accordance with the JIS (the Japanese Industrial Standards) and a correspondingly bright image has to be displayed on the monitor for the medical diagnostic apparatus. In addition, images of very high quality are required in the medical field since an error in the viewing of diagnostic images results in wrong diagnosis. Hence, the artifacts resulting from the forced reduction in gradation resolution can be a serious problem to monitors for medical diagnostic apparatus.
Frame rate control (hereunder referred to as FRC) display is known as a device of solving the problem with image display at reduced gradation resolutions. In this technique, 10-bit image data may be divided by four to give four frames of 8-bit image data which are displayed consecutively to represent a 10-bit gradation in 8 bits. However, this approach suffers from the problem of flicker in the image for the very reason that FRC is performed.
In order to eliminate flicker, the frame frequency in FRC display has to be increased to permit high enough display switching. In practice, however, the driver IC for the monitor and the monitor itself are limited in response speed. This problem presents considerable difficulty in medical applications where an increased number of pixels are used with a view to providing higher image quality by representation of a high-definition image such as QSXGA (2560xc3x972048 pixels).
The present invention has been accomplished under these circumstances and has as an object providing a method which, when displaying an image at a lower gradation resolution than the image data supplied from its source, performs frame rate control (FRC) display to eliminate artifacts and secure a gradation resolution and a brightness resolution that are substantially equal to those of the supplied image data and which method is capable of displaying a high-quality image that is suppressed in visible flicker without any substantial increase in the frame frequency.
Another object of the invention is to provide an apparatus that operates on the method.
The first object of the invention can be attained by a method for displaying an image based on image data supplied from an image data supply source and having a higher gradation resolution than a display, comprising the steps of:
converting the supplied image data to image data for frame rate control display in accordance with a difference in the gradation resolution between the display and the image data;
converting, if substantially identical image data within a specified region has a proportion equal to or greater than a specified threshold, the image data within the specified region to image data assigned an integral multiple of a number of frames in frame rate control; and thereafter
converting the resulting image data to image data for the frame rate control display.
The second object of the invention can be attained by an apparatus for displaying an image based on image data supplied from an image data supply source and having a higher gradation resolution than a display, comprising:
an image display device;
a detection device for detecting a proportion of substantially identical image data within a specified region of the image data;
a data processing device operating based on results of detection by the detection device which, if the proportion is less than a specified threshold, converts the image data within the region to image data for frame rate control display in accordance with a difference in the gradation resolution between the display and the image data and which, if the proportion is equal to or greater than the specified threshold, converts the image data to image data assigned an integral multiple of a number of frames in frame rate control and thereafter converts the resulting image data to image data for the frame rate control display; and
a supply device which supplies successively the image display device with image data processed by the data processing device.
In a preferred embodiment, 10-bit image data is received from the image data supply source, the received image data is converted to 8-bit image data for the frame rate control display and the 8-bit image data is displayed.
In another preferred embodiment, the display has a maximum brightness of 500 cd/m2-5,000 cd/m2.
In further preferred embodiment, the data processing device receives 10-bit image data from the image data supply source and converts the received image data to 8-bit image data for the frame rate control display, and the image display device displays the 8-bit image data.
In still further embodiment, the image display device displays in a maximum brightness of 500 cd/m2-5,000 cd/m2.